Tandem aeronautical propeller



Nov. 10, 1931.

TANDEM AERONAUTICAL PROPELLER Filed Dec. 22, 1928 INVENTOR s. A. REED. 1,831,366

SYLVAN us A. REED.-

ATTORN EY Patented Nov. 10, 1931 UNITED STATES PATENT OFFICEv SYLVANUS A. REED, OF NEW YORK, 'Y., ASSIGNOR TO THE PROPELLER COL, INQ, OF NEW YORK, N. Y., A CORPORATION OF YORK TANDEM AERONAUTIGAL PROPELLER Application filed December 22, 1928. Serial No. 327,764.

My invention relates to tandem aeronauti- 4 mum pitch angles at the blade roots, and then twisted( each blade) in the reverse direction progressively to the tip to establish the pitch I angles appropriate for the different radii. Where a four blade propeller, a six blade propeller, and so on, is required, it is further suggested, in said patents, that two or more such propellers be mounted on a single hub and that the hub structure be appropriately modified to receive them. Nowhere, however, in said issued patents, is there any definite teaching as to the manner in which the tandem blade idea may best be carried out. The present invention, as distinguished from the broad suggestions contained in said patents, relates specifically to a developed means 80 whereby the tandem blade idea as applied to aeronautical propellers may be put to practical use. Not only are the spacing limits of theparallel or tandem blades clearly defined, but in addition, that blade form and that 85 blade angle best suited to a practical tandem or biplane blade aeronautical propeller clearly set forth. Also, as a mounting for said tandem blades, an improved and practical form of propeller hub structure is described and illustrated.

The hub, in its preferred embodiment, comprises a tubular member internally keyed or splined receive the engine shaft, a central flange formed upon said tubular member intermediately of its ends, spacer members (preferably elongated filler blocks) between each face of said flange and the respective opposed faces of the propellers, and bolts assing thru both propellers, both filler'bloc s and said flange, the holes for said bolts being disposed preferably in the long axis of the propeller and at a substantial radius out from said tubular member to minimize torque stresses. Preferably the tandem blades, at their outer ends, and throughout a material portion of their respective lengths, have a depth of chord less than the depth of the gap between said blades, whereas the pitch angles and depth of chord of said blades, at an intermediate point, is such that the leading edge of the rear blade overlaps or extends forwardly beyond the trailing edge of the forward blade notwithstanding the fact that said blades, from end to end, are preferably substantially parallel. I

The advantages of a tandem aeronautical propeller thus characterized will appear from the detail description hereinafter given.

In the drawings, wherein likereference characters denote like or corresponding parts,

Fig. 1 is a plan view of the metal hub about yrlhifh my improved propeller may be assem- Fig. 2 is a section on the line 2-2 of Fig. 1;

' Fig. 3 is a plan view of a spacer member used in assembling my improved propeller;

Fig. 4 is an elevation of the spacer member shown in Fig. 3;

Fig. 5 is a plan view of my improved tandem propeller assembled;

Fig. 6 is a cross section on the center line of the propeller;

Fig. 7 is a cross section on the line 7 7 of Fig. 5; and v Fig. 8 is an elevation of one of the propellers of the assembled propeller, one of the filler blocks being likewise shown in elevation, whereas the tubular member or hub sleeve and the bolts are shown in section.

In Fig. 1 there shown the metal hub (preferably steel) with the tubular part 1 and elongated flange 2 formed thereon intermediately of its ends.

In Fig. 2 the flange 2 is shown in plan and the tubular portion 1 in section. 3 is a keyway formed in said tubular member and 55 are bolt holes formed in said. flange 2 near its outer ends.

The spacer members or hub blocks are preferabl formed of cast aluminum alloy. 66 are bolt holes formed in said blocks to coincide with the bolt holes 5-5 formed in the hub flange; 7 is a central hole, somewhat larger than the tubular member 1 to receive it; and 88 are lightening holes formed in said blocks intermediately of the central hole 7 and the bolt holes 66.

The assembled tandem propeller is made up of propellers 9 and '10, which are fabricated preferably from forged aluminum alloy, somewhat flat in the central part, and twisted in that part to establish the maximum itch angles at the blade roots, the blades ein reversely twisted .progressively from the ade roots out toward the blade tips to establish throughout such portion of the blade length the required pitch. Each propeller has a central hole (undesignated) ormed therein and the propeller 9 is mounted with the hub sleeve or tubular member 1 engaging in said hole at the forward side of the hub flange 2. The propeller 10 is similarly mounted on the rear side of said flange and the spacer members or hub blocks 11 are interposed, one between the pro eller 9 and the hub flange 2, and the other b propeller 10 and the hub flange 2.

In Fig. 7 one of the bolts 4 for fastening the propeller to the hub is clearly shown.

In Figs. 5, 7, and 8, the bolts 44 are clearly indicated. Said bolts pass thru both propellers, both spacer members, and the hub flange, and are secured by nuts 12. 1313 are bevelled bushings and /or washers shaped to the diagonal face of the propellers. .If desired, instead of the propellers 9 and 10 being placed in exact parallelism, a slight stagger may be given them, in which event thehub flange and hub blocks will be modified slightly as to form. I may also have three or more filler blocks and more than one hub flange if and when three or dem, are used. I

As previously stated, the tandem blades are preferably uniformly spaced, altho in that embodiment of'the invention deemed most practical under existing conditions, and the spacing between blades is preferably such that throu hout a portion of the blade lengths in t e vicinity of the blade tips, such spacing or gap exceeds the length or depth of the blade chords (i. e. the distance from the leading edge to the trailing edge of said blade). Moreover, as illustrated in Fig. 5, the blade angle and the depth of chord is preferably such that throughout a portion of the length of the tandem blades the rear propeller 10, along its leading edge, overlaps or extends forwardly beyond the trailing edge more propellers, in tanof the forward propeller. 9.

While I have described my invention in,

detail in its present preferred embodiment, it will be obvious to those skilled in the art etween thev after understanding m invention, that various changes and modi cations may be made therein without departing from the spirit or in uniformly spaced relation, said tandem blades from the inner third of their respective lengths outwardly, having a gradually decreasing depth of chord which, throughout a material portion of the blade lengths in the vicinity of their tips, is less in depth than the depth of the gap between said tandem blades.

2. In an aeronautical propeller, a metal hub including a substantially cylindrical hub sleeve having formed thereon, intermediately of its ends, an outwardly directed flange, tandem blades extending out from said sleeve, one'each, on opposite faces of said flange, and spacer members interposed between said flange and each,said propeller blade.

3. In an aeronautical propeller, a metal hub including a hub sleeve having formed thereon, intermediately of its ends, an outwardly directed flange, opposed tandem blades extending out from said hub sleeve, one each on opposite faces of said flange, the correspondin blades of said opposed tandem bladegroups being united integrally and the propellers formed, in each instance, from a single length of metal, and each said metal length having formed therein an opening thru which said sleeve extends, and means penetrating each blade group and said flange for fastening the propeller to the hub.

4. In an aeronautical propeller, a metal hub including a hub sleeve having formed thereon, intermediately of its ends, an outwardly directed flange, tandem integral propellers having blades extending out from said hub sleeve, one each on opposite faces of said flange, and means engagin said flange' '6. In an aeronautical propeller, a hub in cluding ahub sleeve and carried thereby an elongated outwardly extending filler structure, and unit propellers each having formed therein an opening to receive the hub sleeve, said propellers being disposed respectively on opposite faces of the filler structure where they are fastened.

' the outer ends of said elongated hub.

8. In an aeronautical propeller in which a plurality of tandem propellers each'having a plurality of blades are positioned to rotate with a drive shaft about the axisof said drive shaft, a hub having-an elongated flange extending along the longitudinal axes of the propeller blades and a plurality of elongated spacer elements positioned on opposite sides of the said flange, each of the said spacer elements having a substantiall flat side abutting against the flange an having a curved surface shaped to conform substane tially to the contour of one of the propeller blades and against which the said propeller blade bears.

5 In testimony whereof I hereunto afiix my signature.

SYLVANUS A. REED. 

